Stereophonic sound transmission system



Aug. 5, 1958 R. M. MIKULYAK 2,846,504

STEREOPHONIC SOUND TRANSMISSION SYSTEM Filed Nov. 19, 1956 SOUND SOURCESINVENRDR RM. M/KULYAK wmwzo- United States Patent sTEREoPHoNIc oUNnTRANSMISSION SYSTEM Robert M. Mikulyak, Stirling, N. J., assignor toBell Telephone Laboratories, Incorporated, New York, N. Y., acorporation of New York Application November 19, 1956, Serial No.623,133

6 Claims. (Cl. 179-1) This invention relates to stereophonic soundtransmission systems.

The object of the invention is to provide a sound transmission systemcomprising stereophonic recording and reproduction whereby there isconveyed to the listener the impression that the intelligence is beingcommunicated to him directly from the source.

In accordance with the invention, two directionally sensitivemicrophones are located at the front center of a sound originating areaeach with its axis of maximum sensitivity directed toward a difierentside of the area. The microphones are disposed substantially back toback.

A separate recording-reproducing channel is associated with eachmicrophone. Two separate sound tracks may be recorded and laterreproduced simultaneously through separate amplifier and loudspeakermeans, or each microphone may be directly coupled to its associatedpower amplifier and loudspeakers. In any event, a single loudspeaker isindividually connected to each reproducing channel and located at a sideof the reproducing area corresponding to the position of its associatedmicrophone in the recording area.

A particular feature of the invention resides in the use of intermediatespeaker assemblies disposed in front of the sound reproducing areabetween the single side loudspeakers. Each of these assemblies consistsof two loudspeakers one of which is fed from one channel and the otherof which is fed from the other channel. Each loudspeaker is fed throughattenuating means operative to reduce its output level by an amountcorresponding to the reduction in the pickup of the microphoneassociated therewith as determined by the point on the directionalsensitivity characteristic of the microphone corresponding to thelateral position of the loudspeaker in the sound reproducing area.

The nature of the invention and its distinguishing features andadvantages will be more clearly understood from the following detaileddescription and the accompanying drawings in which:

Fig. 1 is a diagram of a two-channel stereophonic recording systemshowing the outline of the recording area, the relative location of themicrophones and the directional sensitivity characteristic of eachmicrophone at a particular frequency;

Fig. 2 is a diagram showing the volume level patterns of signalsreceived by the microphones and transferred to the loudspeakerassemblies; and

Fig. 3 is a diagram of a two-channel stereophonic reproducing systemshowing the outline of the reproducing area, and the relative locationof the speaker assemblies or groups to which signals received by themicrophones are transferred in accordance with the volume level patternsshown in Fig. 2.

Referring now to the accompanying drawings sound pickups or microphonesA and B are located at the front center of the sound producing area orrecording stage 12, each with its axis of maximum sensitivity, 14 and 16respectively, directed toward a different side of the sound area 12. Inthe embodiment shown in Fig. 1 the microphones are disposedsubstantially back to back, each with its axis of maximum directionalsensitivity at a predetermined angle to the center line of the soundoriginating area, and each associated with a separate recording channel.The microphones are connected by separate transmission lines 18 and 22,and through amplifiers 24 and 26, to recorders 28 and 30, whichcooperate with record media 32 and 34. With this arrangement the outputsof microphones A and B may be recorded on records 32 and 34respectively. Any well-known method may be used to record the outputs ofmicrophones A and B. Recorders 28 and 30 may comprise magnetictransducers and sound record media 32 and 34 may be standard motionpicture film with a recording surface of magnetic oxide.

Curves AM and BM are the directional sensitivitycharacteristics ofmicrophones A and B respectively at a particular frequency. Vector A 0represents the maximum sensitivity of microphone A for the sound sourceat 1, while vector B 0 represents the maximum sensitivity of microphoneB for the sound source at 1. Vectors A 0 and B 0 represent the maximumsensitivity of microphones A and B respectively for the sound source at2, and vectors A 0 and B 0 represent the maximum sensitivity ofmicrophones A and B respectively for the sound source at 3.

As shown in Fig. 3, loudspeaker SA is connected to the reproducingchannel comprising the record medium 32, reproducer 38 and amplifier 40,and is located at a side of reproducing area or stage 42 correspondingto the position of its associated microphone A in the recording area 12.Loudspeaker SB is connected to the reproducing channel comprising therecord medium 34, reproducer 44 and amplifier 46, and is located at aside of reproducing area or stage 42 corresponding to the position ofits associated microphone B in the recording area 12.

There are two playback channels which correspond to the two recordingchannels, and the two sound tracks obtained during the stereophonicrecording are played back simultaneously. However, instead of using onlythe side loudspeakers SA and SB as in a conventional binaural system, amultispeaker system is used. A plurality of reproducing assemblies aredisposed between loudspeakers SA and SB. Each reproducing assemblycomprises two loudspeakers, each connected through an attenuator to adifferent one of the two reproducing channels. The loudspeakers SA, SA2,SA4, SAG, SB, SE2, SE4 and SE6 will have volume levels associated withtheir locations as determined by the curves shown in Fig. 2.

The volume level patterns shown in Fig. 2 are established by plottingthe directional sensitivity of each microphone (over the range frommaximum to zero sensitivity for each sound source) against uniformlyincreased abscissas, the maximum one of which is equal to the length ofthe reproducing area or wall along which the loudspeakers are disposed.The volume level of each loudspeaker in the sound reproducing area willcorrespond to the volume level of sound received by its associatedmicrophone as determined by the point on the directional sensitivitycharacteristic of said microphone corresponding to the lateral positionof the loudspeaker in the reproducing area.

Signals from the three sources 1, 2 and 3 are received by microphones Aand B at the volume levels indicated by A1, A2, A3, B1, B2 and B3. Thesesignals are reproduced by the speaker reproducing assemblies inaccordance with the volume level patterns shown in Fig. 2 wherein thesums of the levels provided by both channels are shown by dotted curves.

Since the lower frequencies have very little efiect on used in theassemblies disposed between the side loudspeakers.

' Moreover, by using two separate loudspeakers fat each intermediateposition, the signals from the two channels are mixed acoustically andany phase diflerence in the signals from the two sound tracks is lesslikely to cause distortion than would be'the case if they were mixedelectronically and reproduced through a single loudspeaker. withacoustical mixing may be lessened by turning for directing theloudspeakers of an intermediate speaker assembly at a slight angle awayfrom each other. The impression of direct communication may be furtherenhanced by interchanging the positions of the speakers in theintermediate assemblies. For example, speaker S136 would occupy theposition occupied by speaker A2 in Fig. 3, and vice versa, and each ofthe speakers would be directed at a slight angle away from the otherwith speaker SB6 turned toward speaker SA and speaker 8A2 turned towardspeaker SB.

As noted heretofore sound tracks need not be recorded and microphone 28may be coupled directly to amplifier 40 and loudspeakers SA, SA2, SA4and SA6, and microphone 30 may be coupled directly to amplifier 46 andloudspeakers SB, S132, SB4 and SE6.

' It is to be understood that the above-described arrangements areillustrative of the application of the principles of the invention.Other arrangements may be devised by those skilled in the art withoutdeparting from the spirit and scope of the invention.

What is claimed is: V

1. A stereophonic sound transmission system'cornp-rising a pair ofdirectionally sensitivemicrophones disposed adjacent each othersubstantially back to back at the front center of a sound originatingarea each with its axis of maximum directional sensitivity directedtoward a different side of said sound originating area, a separatereproducing channel associated with each of said microphones, a soundreproducing area, a loudspeaker connected to each of said reproducingchannels andlocated at a side of said sound reproducing areacorresponding to the location ofits associated microphone in said soundoriginating area, a source of sound in said sound originating area, thevolume level of each of said side loudspeakers corresponding to themaximum volume level of said sound received by its associatedmicrophone, as determined by the directional sensitivity characteristicsof said microphones, a plurality of reproducing assemblies disposedbetween said side loudspeakers, each of said reproducing assembliescomprising two loudspeakers each 2. A stereophonic sound transmissionsystem comprising a sound originating area, a pair of directionallysensitive microphones disposed adjacent each other substantially back toback at the front center of said sound originating area each with itsaxis of maximum directional sensitivity at a predetermined angle to thecenter line of said sound originating area, a separate reproduc- Also,the chance of phase difference distortion ing channel associated witheach of said microphones, a sound reproducing area, a loudspeakerconnected to each of said reproducing channels and located at a side. ofsaid sound reproducing area corresponding to the location of itsassociated microphone in said sound originating area, a source of soundin said sound originating area, the volume level of each of said sideloudspeakers corresponding to the maximum volume level of said soundreceived by its associated microphone, as determined by the directionalsensitivity characteristics of said micro phones, a plurality ofreproducing assemblies disposed between said side loudspeakers, each ofsaid reproducing assemblies comprising two loudspeakers each connectedthrough attenuating means to a .diiferent one of said reproducingchannels, each of said attenuating means being 4. In a stereophonicsound translating system a sound originating area, a source of sound insaid area, a pair 7 of directionally sensitive microphones disposedadjacent each other substantially back to backat'the front center ofsaid sound originating area each with its axis of maximum directionalsensitivity at a predetermined angle to the center line of said soundoriginating area, a separate recording channel connectingeach microphonewith an individual recording device for recording two separate.

phone associated with therecord to be reproduced, the

volume level of each of said side loudspeakers corresponding to themaximum volume level ofsaid sound received by the microphone associatedtherewith, as determined by the directional sensitivity characteristicsof said micro phones, a plurality of reproducing assemblies disposedbetween said side loudspeakers,, each of said reproducing assembliescomprising two loudspeakers eachconnected through attenuating means to adifferent one of said re-.

. producing channels, each of said attenuating means being operative toreduce the output level of its associated loudspeaker by an amountcorresponding to the reduction in,

the pickup of the microphone associated therewith as determined by thepoint on.the directional sensitivity characteristic of said microphonecorresponding to the lateral position of said loudspeakerin said sound-reproducing area. g

5. A sound system in accordance with-claim 4 Wherein the signalsreceived by said microphones are recorded magnetically.

6. A sound system in accordance withclaim 4 wherein the loudspeakers ineachof said reproducing assemblies are angularly disposed, each beingturned away from the other. r

No references. cited.

